1. Field of the Invention
The present invention relates to a photographic element having a neutralizing system for a color diffusion process and particularly to a photographic element comprising a novel timing layer.
2. Description of the Prior Art
Hitherto, it is well known in the color diffusion transfer process to provide a neutralizing layer in order to decrease the pH after transferring diffusible dyes or dye developing agents to a mordanting layer as a result of development using an aqueous alkaline developing solution.
However, if the pH is rapidly decreased by providing a neutralizing layer, the development is interrupted. In order to prevent such a defect, it is also well known to utilize a layer which controls the reduction of the pH with time, namely a "timing layer", together with the neutralizing layer.
A neutralizing system containing these layers can be divided into two types, one type having a timing layer in which the water permeability is inversely proportional to the temperature and the other type having a timing layer in which the water permeability is directly proportional to the temperature.
The term "water permeability" used herein means the property of substantially passing an aqueous alkaline developing solution therethrough and the term "water impermeability" used herein means the property of substantially not passing an aqueous alkaline developing solution therethrough.
In using a timing layer in which the water permeability is inversely proportional to the temperature, the period of time at a high pH (preferably, a pH of about 10 or more) for developing silver halide and forming an imagewise distribution of diffusible dyes increases as the temperature increases. A neutralizing system having a timing layer which is temperature dependent is fundamentally suggested in U.S. Pat. No. 3,455,686. Further, materials for the timing layer, include polyvinyl amide type polymers described in U.S. Pat. Nos. 3,421,893 and 3,575,701. A neutralizing system having a timing layer wherein the above described materials are used where the period of time at high pH increases as the temperature increases is advantageously utilized for the color diffusion transfer process which has the disadvantages that the development rate of the diffusion rate of the dye developing agent is high and excessive amounts of dyes are adsorbed in the mordanting layer at low temperature, such as the color diffusion transfer process described in U.S. Pat. Nos. 2,983,606, 3,415,644 and 3,415,645.
On the other hand, a neutralizing system having a timing layer in which the water permeability is directly proportional to the temperature where the above-described period of time at a high pH decreases as the temperature increases is advantageously utilized for the color diffusion transfer process which uses dye image forming materials which are not diffusible initially but release a diffusible dye as a result of an oxidation-reduction reaction or a coupling reaction thereof with an oxidation product of the developing agent (hereinafter, materials of the former type are called "DRR compounds" and materials of latter type are called "DRR compounds") as described in U.S. Pat. Nos. 3,929,760, 3,928,312, 3,931,144, 3,932,381, 3,993,638 and 4,076,529. Namely, the delay of the development of silver halide and the delay of the above described oxidation-reduction reaction at a low temperature and the deterioration of densities of transferred color images caused by the delay of the diffusion of dyes can be corrected by prolonging the period of time at high pH (namely prolonging the period of time where developing of silver halide and releasing and transferring of the dyes can occur).
Examples of timing layers where the water permeability increases as the temperature increases are timing layers composed of polyvinyl alcohol as described in U.S. Pat. No. 3,362,819, layers described in U.S. Pat. No. 3,785,815 corresponding to Japanese Patent Application (OPI) No. 22935/74 (namely, timing layers containing a water impermeable continuous phase composed of a film forming polymer component produced from an aqueous film forming polymer dispersion and a water permeable heterogeneous phase) and layers described in Research Disclosure page 86, (November 1976) (namely, timing layers formed from a latex of methyl acrylate-vinylidene chloride-itaconic acid copolymers or acrylonitrile-vinylidene chloride-acrylic acid copolymers).
However, in the timing layers described in U.S. Pat. No. 3,785,815, the delay in development can not be sufficiently compesanted for, because the degree of the decrease of the permeability in the low temperature range is small. Further, in the timing layers described in Research Disclosure, supra, there is the defect that the cost of production is high, because it is necessary to use vinylidene chloride which requires special equipment for producing the polymer latex since it is hazardous to humans and gaseous at normal temperature. Further, when the thus-produced latex is used to form a film, it is necessary to use dry air having a high temperature at a step where the film is not sufficiently dried and, consequently, the timing layer causes various defects by rapid vaporizing of water. For example, spots sometimes occur in the resulting photographic images.
Furthermore, the following characteristics are required to a timing layer used in the color diffusion transfer process.
(1) Peeling off between a timing layer and an adjacent layer must not occur. If such peeling off occurs films or film units are cut during the manufacture thereof or developing.
(2) Where a coated surface of a timing layer of a photographic element and a film for heat seal are adhered using a hot melt type adhesive, the adhered surfaces must have a strong adhesion after the heat seal treatment. If the strength of adhesion is small a high speed mass-production of film units utilizing a heat seal treatment is impossible.